This invention relates to stylus devices for use in videographic and like apparatus.
A variety of forms of apparatus are available in which video signals are generated in response to movement of a stylus in contact with the surface of a touch tablet. Usually the stylus is mounted in a holder including a switch which is closed when contact occurs. A pick up coil is mounted near the tip of the stylus to pick up signals from the touch tablet which determine the position of the point of contact of the stylus on the tablet, and when the switch is closed these signals are transmitted to the videographic apparatus, where they are decoded and used to generate an elementary signal representing a picture point in a television type video waveform, the position of the elementary signal in said waveform corresponding to the point of contact. When the stylus is moved to `draw` a line on the surface of the tablet, a train of elementary signals are produced in the video waveform so that, if the video waveform is reproduced in suitable manner, a corresponding line is displayed in the monitor screen.
It has been proposed in U.S. patent application Ser. No. 326,293 to provide the stylus device with a pressure sensitive transducer which produces a signal dependent on the pressure of the stylus on the touch tablet. The signal is fed to the videographic apparatus where it is used to control the magnitude of the elementary signals and thus the intensity of line displayed on the monitor screen.
Other pressure sensitive stylii are disclosed in U.S. Pat. Nos. 3,528,295 and 4,318,096.
In such arrangements the pressure sensitive element comprises a variable resistance which is flexed, compressed or is provided with a sliding contact in order to generate the signal variation dependent on pressure. Because of the generally mechanical nature of this action on the resistance element, the life expectancy and repeatability of operation can be rather limited in view of the substantial use to which the device is subjected.